<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
   .pasent{
       width: 300px;
       height: 200px;
       border: 1px solid orangered;
       position: relative;
   }
   .child{
       height: 50px;
       background: lightblue;
       position: absolute;
   }
    </style>
</head>
<body>
    <div class="pasent">
      <div class="child">
          child
      </div>
    </div>
</body>
</html>